The amounts of different solutes contained in a solvent can generally be determined by a gas chromatograph if the solutes are vaporizable at temperatures not in excess of 400.degree. C. A gas chromatograph is comprised of means for providing a stream of carrier gas, means for introducing solutes from a sample of the solute containing solvent into the stream an oven, a separation column within the oven that elutes the solutes contained in the stream at respectively different times, and a detector for indicating the respective amounts of those solutes as they elute.
An early and widely used means for introducing a sample of solvent into a stream of carrier gas includes a syringe and a heated vaporization chamber through which the stream is made to flow. The temperature of the vaporization chamber is set above the vaporization temperature of the least volatile solute of interest, and a desired volume of sample liquid is injected into the needle of the syringe by operation of the plunger so as to force at least some of the liquid into the vaporization chamber. Non-volatile components in the sample are left in the needle or are deposited on the walls of the vaporization chamber and do not enter the column.
A number of techniques have been developed for operating the syringe, but all of them exhibit discrimination against the less volatile solutes of a sample, i.e., as the volatility decreases below a given value, the amount introduced into the stream decreases. This has led to the suggestion that the needle be left in the vaporization chamber for several seconds so that the solvent and all the solutes in the needle are vaporized, but this does not reduce the discrimination to a level at which it can be ignored. Furthermore, the amount of solutes that reaches the stream of carrier gas varies from injection to injection. Various tedious calibration techniques can be used to compensate for these phenomena. Another difficulty with these injection methods of the prior art is that the vaporization of components in the needle makes it difficult to input sample volumes that are a small fraction of the volume of the needle.
In order to obtain accurate results without employing time-consuming calibration techniques, it is essential that the solutes from a predetermined volume of sample and only that volume be introduced into the stream of carrier gas. This can be done by employing a "cold on-column injection technique" wherein the top of a "T" coupling is inserted in the separating column through which low temperature carrier gas is flowing to the separation column and the sample volume of solvent containing the solutes of interest is injected via the needle of a syringe into the carrier gas through the stem of the T. Unfortunately, however, insoluble components may be present in the sample, resulting in damage to the column. In some cases, the column must be discarded and in others, a piece must be broken off and the remaining portion recalibrated. In addition, this technique is only applicable to very dilute samples and it requires a time-consuming cooling of the oven between injections.
These matters are discussed in an article by K. Grob Jr. and H. P. Neukom, entitled "The Influence of the Syringe Needle on the Precision and Accuracy of Vaporizing GC Injections" which was published during January 1979 in the Journal of HPC and CC at page 15 and in an article by K. Grob and S. Rennhard, entitled "Evaluation of Syringe Handling Techniques for Injection into Vaporizing GC Injectors" which was published during December 1980 in the same journal at page 627.